1. Field of the Invention
The invention relates to a magnet-embedded rotor, a method for manufacturing a magnet-embedded rotor, and an orientation and magnetization device.
2. Description of Related Art
Interior permanent magnet motors (IPM motors) having a structure in which a permanent magnet for a field is embedded in a rotor are known. A method described in Japanese Patent Application Publication No. 2010-193587 (JP 2010-193587 A) is an example of known methods for manufacturing a magnet-embedded rotor used in the IPM motor. In JP 2010-193587 A, a magnet material prior to magnetization is embedded in a magnet insertion hole that is formed in a cylindrical rotor core, and then a magnetization device is arranged to cover an outer periphery of the rotor core. A magnetic flux is supplied into the rotor core from an outer peripheral surface of the rotor core by the magnetization device such that the magnet material embedded in the rotor core is magnetized to become the permanent magnet.
In a case where the magnetic flux is supplied from the outer peripheral surface of the rotor core by the magnetization device as described in JP 2010-193587 A, the quantity of the magnetic flux that can be supplied to the magnet material prior to magnetization embedded in the rotor core is determined by a surface area of the outer peripheral surface of the rotor core and the quantity of the magnetic flux per unit area that can be supplied from the magnetization device. The quantity of the magnetic flux per unit area that can be supplied from the magnetization device is limited. Accordingly, in a case where an area of the outer peripheral surface of the rotor core receiving the supply of the magnetic flux from the magnetization device is small with respect to an area of a magnetization surface of the magnet material, magnetization of a magnetic steel sheet at the site is saturated and it becomes difficult to supply a sufficient magnetic flux to the magnet material, which results in a decrease in the magnetization rate of the permanent magnet. When the magnetization rate of the permanent magnet is decreased, a sufficient magnetic flux is not generated from the permanent magnet, and a magnetic flux density at the outer peripheral surface of the rotor is decreased. This decreases the effective quantity of magnetic flux interlinked to a stator coil, and decreases an output torque of the motor.